Talk politics.

If hydrogen was ever used to replace oil as the transportation of choice, we still have a lot of work to do. It is hardly better than gasoline. Energy density is much lower, so onboard hydrogen storage needs to be improved upon. The car essentially has to be designed in such a way that the throttle is always running at a constant rate (essentially consuming a constant amount of hydrogen) as opposed to energy on demand like gasoline. This requires a great amount of work to be done with batteries and other electricity storage devices. A vast amount of research still needs to be done on catalyst, as a minor imperfection in the hydrogen fuel can cause the complete destruction of the fuel cell, destroying expensive and rare materials.

These issues don't even begin to touch the problems associated with the production and logistics of widespread hydrogen use.